Support poles or posts mounted alongside a roadway have long been recognized as a traffic hazard to motorists traveling on the roadway. As one answer to this hazard, some poles have been given a "breakaway" feature such that the poles break or collapse upon impact with a vehicle. The vehicle thus undergoes a less sharp reduction in speed and the chance and degree of injury to occupants of the vehicle is reduced.
Provision of a breakaway feature in timber utility and traffic support poles presents a special problem. It has been proposed that the poles be weakened by drilling, cutting or otherwise removing part of the pole, and such modifications do give the poles desired breakaway features. However these modifications also leave the pole without the strength needed to resist other forces that a pole commonly experiences, such as snow or ice loads or wind pressures. The result is that the poles have been unable to meet standards specified in the American National Standards Institute: National Electrical Safety Code. Attempts to mechanically reinforce the weakened pole, e.g., by clamping a sleeve around the pole or inserting shims in the recesses of the pole, have proven ineffective, aesthetically unpleasant, and/or too costly.
So far as known, there continues to be no satisfactory technique for giving timber utility and traffic support poles a satisfactory breakaway feature. Accident studies have shown that timber utility poles represent one of the most serious roadside hazards, particularly in urban areas, because of the relatively high frequency with which they are struck and the relatively high severity of these accidents. The problem is increasing as vehicles are reduced in size for energy conservation, thus increasing the need for a less hazardous timber support pole.